The present invention relates to a relay device for selecting a route.
In a network of Ethernet (registered trademark) that has a physical loop, a STP (Spanning Tree Protocol) has been used for preventing endless circulation of data. The STP is a protocol for providing a logical route tree by transferring a control packet called a BPDU (Bridge Protocol Data Unit) among bridges constituting the network based on given priority. To generate the tree, the STP logically blocks ports of bridges unselected on the route.
The STP builds a tree in which a bridge of the lowest bridge priority value is a root bridge and a total value of path costs therefrom is minimal. The BPDU is used for propagating the path costs from the root bridge. In other words, each port of the bridge that has received the BPDU adds its own path cost value to a path cost field of the BPDU, and sends the result to a bridge on a downstream side.
FIG. 18 shows a route selection operation of the STP. In a network model shown in FIG. 18, three bridges 1 to 3 (BRIDGES 1 to 3 shown in FIG. 18) are interconnected through Gigabit Ethernet (registered trademark) (GbES 10 to 12 shown in FIG. 18). The bridges 1 to 3 are connected to the GbES 10 to 12 through physical ports (P11, 12, 21, 22, 31, and 32 shown in FIG. 18, and referred to as ports hereinafter). Specifically, the port 11 of the bridge land the port 31 of the bridge 3 are interconnected through the GbE 10, the port 12 of the bridge 1 and the port 21 of the bridge 2 are interconnected through the GbE 11, and the port 22 of the bridge 2 and the port 32 of the bridge 3 are interconnected through the GbE 12. The bridges 1 to 3 constituting such a network calculate a total path cost of the bridges by using a BPDU that is a control packet (BPDUS 20 to 22 shown in FIG. 18).
In the network model shown in FIG. 18, the bridge 1 of the smallest BP value (BP=2) becomes a root bridge. Here, there are two routes from the bridge 1 to the bridge 3: [1] a route through the GbE 10, and [2] a route through the bridge 2 (route through the GbES 11 and 12). A route selection operation of the STP in this case is as follows.
First, for the route of [1], the bridge 3 is directly connected to the bridge 1. Accordingly, a path cost to be added is only a path cost of the port 31 of the bridge 3 to which the GbE 10 is connected. It is recommended that this path cost be set inversely proportional to a physical link speed (physical band) as in the case of standard specifications (IEEE 802. 1D/1w/1st) shown in FIG. 19. In fact, many Ethernet switches are designed so that values of FIG. 19 can be automatically set in the ports when the STP is operated. Thus, for the port of each bridge, 20 thousand should be set as a path cost because a physical link speed of the GbES 10 to 12 is 1 G[b/s]. Accordingly, a path cost set in the port 31 of the bridge 3 is 20 thousand, and a total path cost of the route [1] becomes 20 thousand.
On the other hand, in the route of [2], a path cost 20 thousand is first added in the port 21 of the bridge 2. Thus, 20 thousand has been set in a path cost field of the BPDU that reaches the bridge 3. A path cost 20 thousand of the port 32 of the bridge 3 is added to this value, and 40 thousand becomes a total path cost.
After the total path cost value has been determined for each route, the total path cost values of the routes are compared with one another, and the route of the smallest total path cost value is selected. In the network model shown in FIG. 18, a total path cost of the route [1] is 20 thousand, a total path cost of the route [2] is 40 thousand, and accordingly the route [1] is selected. As a result, the port 31 of the bridge 3 is selected as a STP tree to permit transfer of a data packet. On the other hand, the unselected port 32 of the bridge 3 is logically set in a blocking state to inhibit transfer of all the data packets.
As described above, based on path costs according to a physical band, the STP forms the tree in which a path cost is minimal. In other words, a scheme is employed in which a route of a band as wide as possible and having a small number of hops is selected as a tree.
Meanwhile, with popularization of wide-area Ethernet (registered trademark) services, the number of highly functional Ethernet switches capable of controlling bands has recently increased. Such a switch can create a logical link of a lower rate in a physical link by using a policer, a shaper, or the like. FIG. 20 shows policing and shaping operations at the bridges. For easier understanding of the description, only a direction from the bridge 1 to the bridge 2 will be considered.
The shaping is for forming a packet stream of a fixed rate or lower in the physical link, i.e., a logical link, by disposing a buffer in the bridge 1 which is a transmission side and limiting reading from the buffer. Thus, an input rate of the bridge 2 that is a reception side becomes equal to a shaping rate of the bridge 1.
The policing is for making the physical link substantially usable only at a policing rate or lower by limiting a communication rate of reception at the bridge 2 that is a reception side. In other words, even when transmission data from the bridge 1 is transmitted at a full wire rate, e.g., 1 G [b/s] of the GbE, packets of the policing rate or higher are discarded by a policing function operated at the bridge 2.
It is to be noted that a virtual port of each bridge for treating the logical link built by the shaping and the policing is referred to as a logical port. Each bridge can treat the logical port as an individual port in one physical port (logical ports 1 and 2 shown in FIG. 20).
The following problems are inherent in the conventional route selection using the STP when the logical link is built by using the highly functional Ethernet switches. FIG. 21 shows the route selection operation of the STP when the logical link is built in the network model shown in FIG. 18.
At the GbE 10, a logical link of 100 M[b/s] is built by shaping operated in the port 11 of the bridge 1. At the GbE 11, similarly, a logical link of 900 M[b/s] is built by shaping operated in the port 12 of the bridge 1. At the GbE 12, a logical link of 900 M[b/s] is built by policing operated in the port 32 of the bridge 3.
In the conventional route selection operation of the STP in such a case, only the physical link speed is taken into consideration as described above, and thus a result is substantially similar to that of the route selection. In other words, the port 31 of the bridge 3 is selected as a tree of the STP, while the port 32 of the bridge 3 is logically blocked.
Thus, a band that is substantially 100 M[b/s] in the GbE 10 is selected, while a band of 900 M[b/s] of the GbE 12 is blocked. In other words, in the conventional route selection operation of the STP, reference is made only to the physical link speed, and thus the tree is selected while a logical band that is a real link width is ignored. This results in selection of a communication band as wide as possible against the STP specifications.
The logical band is built in the physical band in such a manner, for example, when a plurality of users share the physical band. FIG. 22 shows an example of building a plurality of logical links in the network model shown in FIG. 18. In the example shown in FIG. 22, there are two users who wish to set a band between the bridges 1 and 3 (users 1 and 2 shown in FIG. 22), and both require a band of 900 M[b/s] at normal time and a spare band of 100 M[b/s].
When the plurality of users share the physical band as described above, each logical link is allocated to each user, and a spanning tree is built for each user. A MSTP (Multiple STP) or the like is available which can form an independent spanning tree (STI (Spanning Tree Instance)) for each user. According to the MSTP, an independent parameter for a path cost or the like can be provided for each STI, and thus a route different from one user to another can be selected. In other words, according to the MSTP, each user can block a different logical port. However, in the conventional method, a path cost value set as a default value based on the physical band is used. Thus, it is impossible to select a route different for each user.
As a method of avoiding the problem, there is a method involving calculating a path cost matching a logical link rate as shown in FIG. 23, and manually setting a path cost value at each bridge. In the case of using the MSTP, a proper path cost value is manually set at each port of the bridge for each STI as shown in FIG. 22.
However, the method necessitates manual calculation and input of a path cost for each bridge constituting the network. Besides, the logical link building method by the shaping necessitates not only checking of setting in the device but also checking work of opposite device setting because it is a port of the opposite device that is influenced by the path cost. Thus, in the setting of a proper path cost to enable route selection proper for the bridge constituting the network, problems are inherent, i.e., an increase in the number of work steps and complex work.
The following are related arts to the present invention.
[Patent document 1]
    Japanese Patent Laid-Open Publication No. 11-177596[Patent document 2]    Japanese Patent Laid-Open Publication No. 2004-140777